Teletypewriter system



Patented May 17, 1938 UNITED STATES PATENT OFFICE TELETYPEWRITER SYSTEM Application October 6,

7 Claims.

This invention relates to -a teletypewriter sys tem and, more particularly, to a teletypewriter system which includes a subscribers station circuit for enabling operationover longer lines than would otherwise be possible without the use of a telegraph repeater, all other conditions being equal.

Heretofore, when a subscribers teletypewriter station has been located at a considerable distance from its associated teletypewriter central oflice, it has ordinarily beennecessary to connect a telegraph repeater into the line between the central .ofiice and the subscribers station. In a widespread communication system, it has often been necessary to employ a considerable number of such telegraph repeaters. Since each repeater costs several hundred dollars-the total cost of all the repeaters used in a large communication systern is quite high.

Accordingly, it is an object of this invention .to obviate the need for using as many telegraph repeaters in a communication system as has heretofore been necessary.

It is also an object ofthis invention to obviate the need for abreak relay at a subscribers teletypewriter station thereby avoiding the initial costof such a relay and the expense of its maintenance.

It is a further object of this invention to enable the subscribers teletypewriter to print a home copy of all messages transmitted notwithstanding the elimination of the break relay usually employed at a subscribers station.

These objects of the invention are accomplished, in a telegraph system having only a onewire line with a ground return for connectingthe subscribers station to the central ofiice, by providing separate sending and receiving loops at the subscribers station connected togetherby the subscribers set of sending contacts. This provision of separate sending and receiving loops eliminates .the need for a break relay at the sub scribers station. To provide the subscriber with a home copy of transmitted messages, it is necessary that the sending and receiving loops be connected together through the subscribers set of sending contacts to battery. With this arrangement, the operation of the subscribers sending contacts will open both the sending and receiving loops thereby transmitting the signalboth to the subscribers printer magnet and also out over the line to the central oifice. This permits local, as well as distant, reception of messages transmitted by the subscribers printerand, at the same time, eliminates the need for a break relay which would 1936, Serial No. 104,184

ordinarily be required for a single, or.common, sending and receiving loop of usual design.

In the subscribers station circuit, two potentiometers are bridged across the local source of power supplywhich may include either a motorgenerator or rectifier. The mid-point of the resistance of one potentiometer is connected to ground to provide the effect of two polarities; i. e., positive and negative voltage with respect to ground as will ,be explained hereinafter. The resistance element of the subscribers artificial line, or balancing network, is connected to the mid-point of the resistance element of the other potentiometer instead of being connected directly to ground in the usual manner. This enables the artificial line currents to return to the local power supply source by a separate metallic path instead of through the grounded potentiometer throughwhich the line currents pass. This increases the voltage appliedto the line with respect to ground, as will be explained hereinafter, thereby permitting operation over longer lines than would otherwise be possible all other conditions being equal.

These and other features of the invention will be described more fully in connection with the following detailed description of the drawing in which:

Fig. 1 represents a subscribers teletypewriter station connected by a one-wire telegraph line having a ground return to receiving teletypewriter apparatus at a central office;

Fig.2 illustrates a subscribers teletypewriter station which is somewhat similar to that shown .in Fig. 1 but which is connected to receiving teletypewriterapparatus at a central oflice by atwopath metallic circuit;

Fig. 3 shows a noise suppressor suitable for use at the subscriber's station shown in Fig. 2 when the two-path metallic circuit includes an openwire line; and

Fig. 4 represents a noise suppressor suitable for use at the subscribers station shown in Fig. 1 whenthe two-path metallic circuit includes a cable line.

It is to be understood that the circuits shown in the drawing are presented for the purpose of illustrating principles of the invention and that the invention is not restricted to the particular circuits shown. The central office may be of any suitable construction such as that described in Patent 2,028,818; granted January 28, 1936, to R. J. Anspach et al. The disclosure of this Anspach et al. patent is incorporated herein by reference as a part of this specification.

tions.

After traveling through the receiving apparatus at the central ofiice, the line circuits pass through other equipment at the central ofiice and then out over other lines leading either to other teletypewriter central offices or to other subscribers teletypewriter stations. The central office equipment and the line circuits may be of any suitable design, such as that disclosed in a copending application filed Oct. 29, 1936, by W. V. K. Large and G. A. Locke and having Serial No. 103,154.

In Fig. 1, there is represented in schematic form a subscribers teletypewriter station I connected to a central ofiice 2 by a one-wire telegraph line 3, which, as is indicated in the drawing, leads through the equipment at the central ofiice 2 to other lines extending either to other central offices or to other subscribers teletypewriter stations. It is to be understood that line 3 may be any suitable type of line, such as a composite line. The subscribers station I is shown to be provided with the usual Well-known equipment including sending contacts 4, printer magnet 5, break key 6, recall key 1, local source of power supply 8, and rectifier 9.

The receiving relay II) at the subscribers station I has one side of its lower winding connected to the balancing network or artificial line II which is, in turn, connected to the mid-point of the resistance element of potentiometer I2. The line circuit leads from the upper winding of receiving relay I through noise suppressor I3, over the armature of the subscribers sending relay I4,

and then through a portion of potentiometer I to ground I6. Incoming signals from line 3 will pass through receiving relay I0 and will cause it to actuate its armature to open and close the receiving loop which leads from the positive output terminal of rectifier 9 to the contact and armature of receiving relay Ill, through the winding of printer magnet 5, sending contacts 4, break key 6, and then to the negative output terminal of rectifier 9.

The subscribers sending loop leads from the positive output terminal of rectifier 9, through the upper winding of sending relay I4, sending contacts 4, break key 6, and then to the negativeoutput terminal of rectifier 9. Opening of this sending loop by the sending contacts 4 will cause the sending relay I4 to actuate its armature thereby applying either positive or negative voltage to the line circuit.

At the central office 2, the line circuit leads from line 3 through the upper winding of receiving relay I I and then the line current divides, one portion passing through the lower winding of receiving relay I1 and then through the balancing network, or artificial line, I8 to ground. The other portion of the line current passes over the armature of the sending relay I9 and then to grounded battery 20. Variations in the line cur- .rent effected by operation of sending contacts 4 will cause receiving relay I! to move its armature back and forth to apply either positive current from battery 2! or negative current from battery 2|] (after the current has passed from battery 20 over the armature of the break relay 22) to the circuit leading from the armature of receiving relay I! through the upper winding of break relay 22, upper winding of the sending relay I9, and then out through the rest of the central office equipment to other lines leading either to other central offices or to other subscribers sta- The rest of the central ofiice equipment and the other lines with their associated central oflices and subscribers stations have not befin subscribers receiving relay shown in the drawing for the sake of simplicity. As was stated above, these may be of the type shown in the copending application of Large et al. identified above.

In the operation of the system, when the subscriber wishes to transmit a message, he opens and closes his sending contacts 4. The subscribers sending relay I4 follows the opening and closing of contacts 4 and moves its armature back and forth between its contacts to apply either negative or positive voltage from rectifier 9 to the line circuit which, as is shown in the drawing, has a ground return path to ground I6 at the midpoint of potentiometer I5. Thus, by means of grounded potentiometer I5, the subscriber is able to alternately apply positive and negative voltages from his rectifier 9 to line 3. This produces a change in the current flowing in line 3 and operates the receiving relay I? at central ofiice 2. Due to the sending contacts 4 being also connected into the subscribers receiving loop, the It will follow the opening and closing of contacts 4 thereby causing the subscribers teletypewriter to make a record, or home copy, of the messages that he transmits.

The subscribers circuit arrangement combines the functions of a subscribers station set and a toll line terminal repeater. It requires little more apparatus than the station set alone and is designed to operate on power furnished by the rectifier 9. Although a single polarity rectifier 9 has been shown with a potentiometer I5 to secure its mid-point, equally good results may be obtained by using a two-polarity rectifier having its mid-point grounded.

through the artificial line II to potentiometer i2.

Potentiometer I2 thus provides a return path to rectifier 9 for the artificial line currents which is separate from the path followed by the line currents in the ground return path through potentiometer I5 thereby avoiding objectionable voltage drops in potentiometer I5. This increases the current in line 3 thereby permitting operation over longer lines than would otherwise be possible without using a repeater and using a given generator operating at a given speed with a given impedance drop. Thus, the subscribers station circuit requires two less telegraph relays than would a repeater using the standard balanced loop circuit.

The currents flowing in the two windings of receiving relay I 0 oppose each other. When a marking signal is transmitted by relay I4, the current in the upper winding of relay II) will be larger than the current in the lower winding and will consequently cause the armature of relay ID to be held on its marking contact. When a spacing signal is transmitted by relay I4, the current in the upper winding of relay II] is decreased below the level of current in the lower winding. This will hold the armature of relay I9 on its marking contact as the current in the lower, Or artificial line, Winding has been reversed.

In summary, it can be seen that the subscribers. sending contacts 4 control the circuit through the printer magnet 5 as well as through the sending relay I4 so that the subscribers teletypewriter prints a record of whatever is transmitted. It can thus be seen that the printer magnet is under the control of both the receiving relay I0 and the sending contacts 4 of the subscribers teletypewriter and operates on open and closed signals in either case.

During the time that the subscriber is transmitting a message, an operator at the central oifice 2 may take control of the circuit by operating his break key (not shown) which opens the circuit leading through the upper windings of the sending relay I9 and break relay 22. The resulting operation of the armatures of these relays causes a spacing signal to be transmitted to the subscribers station I. The arrival of this spacing impulse at station I causes the receiving relay II) to operate its armature to its spacing contact. This opens the subscribers receiving loop through the printer magnet 5 thereby stopping the printing, by the subscribers teletypewriter, of the home copy of the message being transmitted by him.

After the subscriber has finished transmitting messages to the central ofiice 2, he may, at some later time, recall the operator by momentarily operating his recall key I which is of the makebefore-break type. The operation of recall key 'I maintains the subscribers local sending and receiving loops closed and energized, but opens line 3. This opening of line 3 effects the operation, in a well-known manner, of the usual recall lamp (not shown) at the central office 2 which serves to attract the attention of the operator.

Signals transmitted from central office 2 to subscribers station I cause the sending relay I9 to actuate its armature which fluctuates between its marking and spacing contacts to transmit polar reversals of current through the apex of the central ofiice receiving relay II. As the artificial line I8 is adjusted to closely simulate the impedance of the actual line 3 and its terminal equipment at station I, the current from relay I9 divides between the upper and lower windings of relay I! which are series opposing with respect to the outgoing current.

When a marking signal is being transmitted from central office 2, the current in the upper, or line winding, of relay I1 is the larger due to the aiding polarity of voltage applied to line 3 at station I. This holds the armature of relay I! on its marking contact, and the armature of relay II] will also remain on its marking contact.

When a spacing signal is transmitted, the voltage applied to the line opposes that applied at station I and reduces the current flowing in the upper winding of relay I! to a lower level than that flowing in the lower, or artificial line, winding. At the same time, the current in the lower winding of relay I I is reversed, thereby causing the armature of receiving relay I! to be held on its marking contact. When the normal line current is reduced by the application of a spacing voltage at the central ofiice, the armature of the receiving relay III at station I will be operated to its spacing contact by the current flowing in its artificial line winding.

During the transmission of signals from central office 2 to the subscribers station I, the subscriber can interrupt and take control of the communication circuit by operating his break key 6. This opens the operating circuit of his printer magnet 5 thereby preventing printing by his teletypewriter. The operation of break key 6 also opens the circuit through the upper winding of sending relay 14 thereby allowing the biasing current in the lower winding to cause relay I4 to operate its armature to its spacing contact. This applies spacing, or negative, voltage to line 3 and causes the armature of relay I! at central office 2 to be operated to its spacing contact. Consequently, the current in the loop passing through the upper windings of the sending and break relays I9 and 22 is reduced to zero thereby interrupting transmission to station I.

In addition to saving the expense of providing and maintaining the usual break relay at the subscribers station I and saving the expense of a repeater connected in series with the line 3, the circuit described above possesses the advantage of providing high quality transmission in both directions. Furthermore, the operating voltages at the subscribers station I are approximately one-half those employed at central ofiice 2 because of the grounded potentiometer I5 bridged across the output terminals of rectifier 9. This reduces the unbalance effects at station I, due to line leakage, sufficiently to permit the use of a fixed balance artificial line at station I for communication lines of moderate length. Although the use of a fixed balance artificial line at station I increases the unbalance effects of leakage at the central ofiice 2, repeaters with adequate balancing facilities are provided at central oflice 2 for compensating for these unbalance eflects.

A subscribers station set arranged for twopath polar operation is shown in Fig. 2. The outstanding feature of this station set is that it permits transmission of positive and negative l25-volt signals from a single polarity nongrounded power supply source by means of a single relay whereas full commutation arrangements of usual design generally require two relays.

Transmission of messages from the central ofiice I02 to the subscribers station I BI is accomplished by opening and closing the loop circuit through the upper windings of the sending and break relays H9 and I22. tion of the armature of the sending relay H9 transmits polar reversals out over the line I 03 which are received at station IOI by the receiving relay III] connected in series with line I113.

The resulting operation of the armature of relay Ilil opens and closes the subscribers receiving loop through the printer magnet I05.

When the subscriber sends messages to the central office, the operation of his sending con tacts I04 will open the sending loop connected through the upper winding of the sending relay H4. The resulting operation of the armature of relay H4 alternately applies positive and negative 125 volts to the line I03 thereby operating the receiving relay Ill at central ofiice IE2. This is accomplished as follows: when the sending contacts I04 are closed, the armature of the subscribers sending relay I I4 is on its marking contact and positive current will flow from the armature of the sending relay III! through the noise suppressor and over line I63 thereby holding the armature of receiving relay IIl at central ofiice I02 on its marking contact. This current returns to station IUI over a ground return path and through resistance I2'I to the negative terminal of the generator I09.

When the sending contacts I04 are opened, the armature of the sending relay I I4 is operated to its spacing contact and negative current will flow through resistance I34 and out over line I03 The resulting operato operate the armature of the receiving relay H1 at central ofiice I02 to its spacing contact. This current returns to station IllI over the ground return path to the positive side of the generator I09 which is grounded by the spacing contact of the sending relay II4. Positive and negative voltages of full generator voltage are therefore applied alternately to the line I03 by means of a single transmitting relay I I4. When the resistance IZI equals resistance I34 the terminal impedance for marking equals the terminal impedance for spacing thereby insuring unbiased transmission of signals to the central office I02.

When line IE3 is an open-wire line, the noise suppressor I23, shown in Fig. 3, should be connected into the circuit, shown in Fig. 2, at the points indicated by the letters a and 1). Noise suppressor I23 comprises an inductance I24, connectible in series with the line circuit, and a resistance I25, connectible in parallel with the line circuit, connected to a grounded condenser I26.-

On the other hand, if line I03 is a cable line, the cable line noise suppressor I28, shown in Fig. 4, should be connected into the circuit of Fig. 2 at the points a and 1). Noise suppressor I28 includes two inductances I29 and I30 connectible in series with the line circuit and having their mid-point connected to a resistance I3I and grounded condenser I32. In addition, a condenser I33 is bridged across the inductance I39. This cable line noise suppressor I28 is very effective in preventing noise in telephone circuits operating over the same line circuit and also permits a high degree of quality in the transmission of telegraph messages.

What is claimed is:

l. A teletypewriter system having in combination a telegraph line, a subscribers teletypewriter station connected thereto, said subscribers teletypewriter station having a receiving loop with a receiving magnet connected therein, a sending loop with a sending relay connected therein, a source of power supply, and means for simultaneously applying the source of power supply to both a winding of the receiving magnet and a winding of the sending relay, said means including an operative connection between the source of power supply and the receiving magnet and the sending relay.

2. A teletypewriter system having in combination a telegraph line, a subscribers teletypewriter station connected thereto, said subscribers teletypewriter station having a receiving loop with a receiving magnet connected therein, a sending loop with a sending relay connected therein, a source of power supply, and means for simultaneously applying the source of power supply to both a winding of the receiving magnet and a winding of the sending relay, said means including a set of sending contacts.

3. A teletypewriter system having in combination a telegraph line, a subscribers teletypewriter station connected thereto, said subscribers teletypewriter station having a receiving relay connected into the telegraph line, a receiving loop with a receiving magnet connected therein, a sending loop with a sending relay connected therein, a source of power supply, and interconnecting instrumentalities for simultaneously applying the source of power supply to both a winding of the receiving magnet and a winding of the sending relay, said interconnecting instrumentalities including sending means.

4. A teletypewriter system having in combination a telegraph line, a subscribers teletypewriter station having a potentiometer having a negative side and a positive side, a receiving relay provided with two windings, one of said windings being connected into the telegraph line and the other of said windings being connected to the mid-point of the potentiometer, a source of power supply having a negative terminal and a positive terminal, control means for applying voltage from either terminal to the telegraph line, and means for increasing the voltage applied to the line, said means comprising two electrical conductors, one connecting the negative side of the potentiometer directly to the negative terminal of the source of power supply and the other connecting the positive side of the potentiometer directly to the positive terminal of the source of power supply.

5. A teletypewriter system having in combination a telegraph line, a subscribers teletypewriter station having a potentiometer having a negative side and a positive side, a receiving relay provided with two windings, one of said windings being connected into the telegraph line and the other of said windings being connected to the potentiometer, a grounded potentiometer connected across the terminals of the source of power supply, control means for applying voltage from either terminal to the telegraph line, and means for increasing the voltage applied to the line, said means comprising two electrical conductors, one connecting the negative side of the potentiometer directly to the negative terminal of the source of power supply and the other connecting the positive side of the potentiometer directly to the positive terminal of the source of power supply.

6. A teletypewriter system having in combination a telegraph line, a subscribers teletypewriter station connected thereto, said subscribers teletypewriter station having an artificial line, a receiving relay provided with two windings, one of said windings being connected into the tele graph line, and the other of said windings being connected to the artificial line, a source of power supply having a negative terminal and a'positive terminal, control means for applying voltage from either terminal to the telegraph line, and means for increasing the voltage applied to the line, said means comprising a resistance bridged across the terminals of the source of power supply and an electrical conductor for connecting the artificial line to the mid-point of said resistance.

'1. A teletypewriter system including a teletypewriter central office, a subscribers teletypewriter station, a two-path circuit connecting the subscribers station to the central oiiice for the transmission of polar telegraph signals, said subscribers station having a single non-grounded power supply, and control means for applying positive and negative voltage from the power supply to the two-path metallic circuit, said control means including a single transmitting relay.

WALTER W. CRAMER. GEORGE C. CUMMINGS. 

